The present invention is directed to radio direction finding systems, and more particularly to a novel and improved radio direction finding system including a novel memory feature for storing directional data corresponding to the direction of arrival of a plurality of radio signals for display upon command.
While the invention may find utility in a variety of applications, the disclosure will be facilitated by particular reference to a radio direction finding system and in particular, a marine automatic direction finding (ADF) system. A direction finding system generally comprises a radio receiver including circuits for determining the direction of arrival of a received radio signal and an indicator or display for producing a display or an indication of this directional information. It will be appreciated that determination of the direction of arrival of the signal correspondingly permits determination of the direction of the source of the transmission of the radio signal relative to the receiver.
Such direction finding devices have developed in the prior art over a number of years. Initially, at least two receivers at different locations were utilized to receive the same signal, whereupon an operator could determine the direction of the originating source of transmission of a received radio signal by triangulation methods. Other prior art devices utilized different antenna configurations and antenna arrays to determine the direction of arrival of a received radio frequency signal. Some such systems utilize two or more relatively simple antennas, while some require physically large and expensive antenna arrays, which are either manually or electronically switched. In either case, the antenna or antennas were coupled to signal processing circuits to extract directional information from the received signals. A display of the processed received information was then obtained in a variety of different ways, such as utilizing electromagnetic coils to operate a directional compass, auto compasses, cathode ray tube displays, or the like.
Moreover, the prior art has been mainly concerned with determining the direction of arrival of but a single received radio signal for immediate display only. Accordingly, if a signal were of brief duration, or a notation was not made of direction during the display thereof, the direction of arrival of a given signal might be irrevocably lost. Hence, to monitor the directions of two or more signals, many prior art devices require that notations be made as to the direction of the first signal to be monitored before commencing to monitor the direction of the second or other further signals.
Additionally, it is often desirable to receive and monitor the direction of emergency signals received on the emergency channel and sometimes known as the emergency position indicating radio beacon (EPIRB). Many direction finding systems of the prior art have failed to make provision for specialized additional decoding and monitoring of the direction of such emergency or "EPIRB" signals, or to give priority to such monitoring.